<?php
namespace classlib\crypt;
class xxtea {
	/**
	 * 使用一个密钥对数据进行可逆加密
	 * @param string $str
	 * @param string $key 默认值
	 * @return string 加密的密文 base64
	 */
	public static function encrypt($str, $key='%*(A^G*(&^*&&D&%F*(S') {
		if ($str == '') {
			return '';
		}
		$v = self::str2long($str, TRUE);
		$k = self::str2long($key, FALSE);
		$n = count($v) - 1;
		
		$z = $v[$n];
		$y = $v[0];
		$delta = 0x9E3779B9;
		$q = floor(6 + 52 / ($n + 1));
		$sum = 0;
		while (0 < $q--) {
			$sum = self::int32($sum + $delta);
			$e = $sum >> 2 & 3;
			for($p = 0; $p < $n; $p ++) {
				$y = $v[$p + 1];
				$mx = @self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ @self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
				$z = $v[$p] = self::int32($v[$p] + $mx);
			}
			$y = $v[0];
			$mx = @self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ @self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
			$z = $v[$n] = self::int32($v[$n] + $mx);
		}
		$str = self::long2str($v, FALSE);
		$str = base64_encode($str);
		return $str;
	}
	
	/**
	 * 利用固定密钥解密资料信息
	 * @param string $str
	 * @param string $key
	 * 
	 * @return string 返回资料明文
	 */
	public static function decrypt($str, $key='%*(A^G*(&^*&&D&%F*(S') {
		if ($str == "") {
			return "";
		}
		$str = base64_decode($str);
		$v   = self::str2long($str, FALSE);
		$k   = self::str2long($key, FALSE);
		$n   = count($v) - 1;
		
		$z   = $v[$n];
		$y   = $v[0];
		$delta = 0x9E3779B9;
		$q   = floor(6 + 52 / ($n + 1));
		$sum = self::int32($q * $delta);
		while ($sum != 0) {
			$e = $sum >> 2 & 3;
			for($p = $n; $p > 0; $p --) {
				$z = $v[$p - 1];
				$mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
				$y = $v[$p] = self::int32($v[$p] - $mx);
			}
			$z = $v[$n];
			$mx = self::int32((($z >> 5 & 0x07ffffff) ^ $y << 2) + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::int32(($sum ^ $y) + ($k[$p & 3 ^ $e] ^ $z));
			$y = $v[0] = self::int32($v[0] - $mx);
			$sum = self::int32($sum - $delta);
		}
		return self::long2str($v, TRUE);
	}
	
	/**
	 * 整形转字符串
	 * @param unknown_type $v
	 * @param unknown_type $w
	 */
	private static function long2str($v, $w) {
		$len = count($v);
		$s = array();
		for($i = 0; $i < $len; $i ++) {
			$s[$i] = pack("V", $v[$i]);
		}
		if ($w) {
			return substr(join('', $s), 0, $v[$len - 1]);
		} else {
			return join('', $s);
		}
	}
	
	/**
	 * 字符串转整形
	 * @param unknown_type $s
	 * @param unknown_type $w
	 */
	private static function str2long($s, $w) {
		$v = unpack("V*", $s . str_repeat("\0", (4 - strlen($s) % 4) & 3));
		$v = array_values($v);
		if ($w) {
			$v[count($v)] = strlen($s);
		}
		return $v;
	}
	
	/**
	 * 工具函数转成32位整形
	 * @param int $n
	 * @return int
	 */
	private static function int32($n) {
		while ($n >= 2147483648) {
			$n -= 4294967296;
		}
		while ($n <= - 2147483649) {
			$n += 4294967296;
		}
		return (int)$n;
	}
}